Coexistence of the Three Trophic Levels in a Model with Intraguild Predation and Intraspecific Competition of Prey

The model of a three-trophic community with intraguild predation is considered. The system consists of three coupled ordinary differential equations describing the dynamics of resource, prey and predator. Models with intraguild predation are characterized by predators that feed on resource of its own prey. A number of similar models with different functional responses have been proposed. In contrast to previous works, in the present model, the predator functional response to the resource is differed from that to the prey. The model takes into account an intraspecific competition of prey to stabilize the system in resource-rich environment. Conditions of existence and local stability of non-negative solutions are established. The possibility of Hopf bifurcation around positive equilibrium with consumption rate as bifurcation parameter is studied. For the model, in the plane of the consumption and predation rates, the regions of existence and stability of boundary and internal equilibria are constructed. Numerical simulations show that the region of equilibrium coexistence of populations is increased due to the inclusion of prey self-limitation in the model. Bifurcation diagrams confirm the stabilizing effect of intraspecific competition of prey on the system dynamics in resource-rich environment.

Computer Simulation of Shear-Induced Phase Separation and Rheology in Two-Component Viscoelastic Fluid

We numerically study the dynamics of polymer solutions in two dimensions at a temperature above the equilibrium coexistence curve under shear flow. Our model is based on the Lagrangian picture of fluid dynamics. We can incorporate viscoelastic effects into the model by introducing a kind of fluid particles which have memories of their own past history. We carry out computer simulations and observe that shear-induced phase separation occur and the system shows a shear thinning rheological property. The most remarkable result is that the dependence of normal stress coefficient on shear rate changes at a shear rate which is comparable to inverse of the stress relaxation time. Our results imply that the shear-induced phase separation can change qualitative features of rheological response.

Phyllocladus aspleniifolius: Variability in the Population Structure, the Regeneration Niche and Dispersion Patterns in Tasmanian Forests

This study aimed to determine the range of the regeneration niches of Phyllocladus aspleniifolius (Podocarpaceae) in terms of differential microsite occupation, population structure and dispersion pattern at 50 sites. The distribution and sizes of stems were mapped on belt transects to within 0.5 m, and the microsites of seedlings and saplings were recorded. A variety of population structures exist and are related to community floristics and structure. Community variation provides different microsite opportunities. Phyllocladus aspleniifolius showed a preference for elevated sites, including logs, buttresses and old stump mounds. Aggregation of regeneration is common and is determined by microsite distribution and seed dispersal characteristics. It is concluded that although the regeneration of P. aspleniifolius is favoured by catastrophic disturbance, smaller scale processes such as those evoked in the concept of non-equilibrium coexistence are likely to allow P. aspleniifolius to persist in all communities throughout its range in the absence of large scale disturbances.